Photographic silver halide lith material

ABSTRACT

A method is provided of producing high contrast images by development at a temperature above 30*C of an exposed photographic light-sensitive lith-material comprising a support having thereon at least one light-sensitive silver halide emulsion, which comprises at least 50 mole percent of silver chloride and at least 5 mole percent of silver bromide, wherein the said material comprises a disulphide compound of the formula:

United States Patent [191 Hofman et al.

[4 1 Dec. 16, 1975 PHOTOGRAPHIC SILVER HALIDE LITH MATERIAL [75] Inventors: Emiel Alexander Holman, Mortsel;

Jules Robert Berendsen, Deurne; Robert Joseph Pollet, Vremde, all of Belgium [73] Assignee: Agfa-Gevaert, N.V., Mortsel,

Belgium [22] Filed: Aug. 11, 1972 [21] Appl. No.: 279,795

[30] Foreign Application Priority Data Sept. 13, 1971 United Kingdom 42562/71 [52] US. Cl 96/66.5; 96/109 [51] Int. Cl. 603C 5/30; (303C 1/34 [58] Field of Search 96/66.5, 109, 66, 66.3

[56] References Cited UNITED STATES PATENTS 3,043,696 7/1962 Herz et al. 96/109 3,057,725 10/1962 Herz et al. 96/109 3,062,654 11/1962 Allen et al. 96/109 3,226,232 12/1965 Dersch et al 96/109 3,397,986 8/1968 Millikan et al... 96/109 3,447,925 6/1969 Dersch et al 96/665 3,573,914 4/1971 Masseth 96/66 3,615,488 10/1971 Drago 96/66 3,615,527 10/1971 Nishio et al 96/66.3

3,640,715 2/1972 Hiickstiidt 96/66.5 3,647,469 3/1972 Hiickstadt 96/109 Primary Examiner-Mary F. Kelley Attorney, Agent, or FirmA. W. Breiner [57] ABSTRACT A method is provided of producing high contrast images by development at a temperature above 30C of an exposed photographic light-sensitive lith-material comprising a support having thereon at least one light sensitive silver halide emulsion, which comprises at least 50 mole percent of silver chloride and at least 5 mole percent of silver bromide, wherein the said material comprises a disulphide compound of the formula:

These disulphide compounds reduce fog formation upon processing at elevated temperature without decreasing the emulsion speed to a noteworthy extent.

8 Claims, No Drawings 1 PHOTOGRAPHIC SILVER HALIDE LITH MATERIAL This invention relates to development at increased temperature of exposed high contrast silver halide emulsions for graphic arts, more particularly high contrast silver halide emulsions of the lith type.

In the photomechanical arts, photographic films capable of providing high image Contrast are required for the preparation of the line and halftone film intermediates which are used in making printing plates. In reproducing continuous tone material, it is customary to make a halftone photographic intermediate, usually a film negative, in which the gradations in tone are represented by different sizes of dots of uniform density. The shape, density and uniformity of the halftone dots are closely correlated to the quality of the resulting picture.

Lith emulsions, which are widely used for line and screen photography, have a chracteristic curve with a short toe and high gamma and produce sharply defined images with high density extending to the edges of lines and dots. This applies especially when the lith type developer is used, which comprises as the only developing agent hydroquinone or a hydroquinone derivative, and which has a very low sulphite ion content, the sulphite ion content being maintained at a low and a constant value by the addition to the sulphite containing devel oping solution of formalin (paraformaldehyde) or by the direct addition to the solution of the addition product of sulphite and formalin viz. formaldehydebisulphite. Though lith emulsions are preferably developed in lith -type developers they can also be developed in conventional highcontrast developers such as a Metolhydroquinone developer, or a developer composition of the kind described in copending U.S. application Ser. No. 426,134 filed Dec. 19, 1973, which is acontinuation of U.S. application Ser. No. 226,232 filed Feb. 14, 1972 Development of exposed photographic silver halide materials including lith materials normally occurs at ambient temperature (about 20C). Whereas, in careful tray processing the development time is of minor importance, it is desirable in machine processing to reduce the time of processing, which can be done by carrying out processing at elevated temperatures, say above 30C. However, development at elevated temperatures causes a substantial increase in fog, which cannot be reduced sufficiently by means of the conventional antifoggants or emulsion stabilizers e.g. heterocyclic mercapto compounds such as l-phenyl-S-mercapto-tetrazole and azaindenes such as 5- methyl-7- hydroxy-s-triazolo-[ l,5-a]pyrimidine.

It has now been found that the fog produced in lith emulsions by processing at temperatures above 30C can be reduced without a noteworthy decrease of emulwherein:

each of'A, and A represents alkylene, preferably C C; alkylene which may be substituted e.g. by alkyl and aryl, arylene e.g. phenylene which may be substituted e.g. by alkyl, alkoxy, halogen or a water-solubilizing group e.g. sulpho and carboxyl in acid or salt form, or a bivalent heterocyclic group, and

each of X and Y represents a water-solubilizing group e.g. sulpho and carboxyl in acid or salt form or a substituent carrying such water-solubilizing group, the said substituent forming a bridging group between the water-solubilizing group and A, or A and may be a saturated or unsaturated aliphatic group, e.g. alkyleneoxy, alkyleneoxycarbonyl, vinylene, alkyleneoxycarbonylvinyl, alkylenecarbamoyl, alkylene sulphamoyl, alkylene amino and alkylene acylamino; an aromatic group e.g. phenylene, phenylene carbamoyl, phenylene sulphamoyl and phenylene acylamino; or a heterocyclic group eg benziniidazolylene.

The lith emulsions used according to the present invention are high contrast fine grain silver halide emulsions which contain at least about 50 mole percent of silver chloride and at least about 5 mole percent of silver bromide. If desired, the silver halide can also contain a small amount of silver iodide; this amount is less than about 5 mole percent and preferably less than 1 mole percent. Y Y

The present invention thus provides a method of developing at a temperature above 30C an exposed lith type of silver halide material ,-.of the kind described above that comprises a disulphide compound corresponding to the above general formula.

Though the conventional alkaline-,"pi'ire hydroquinone, low free sulphite developerpis.v advantageously used to develop the exposed lith emulsions of the invention, a hydroquinone developer having a high content of alkali sulphite, e.g. a Metol-hydroquinone developer or a developer of the kinddescribed in the cognate co-pending U.S. application Ser. No. 426,134 filed Dec. 19, 1973, which is a continuation of U.S. application Ser. No. 226,232 filed Feb. 14, 1972 may also be used. In these types of developers the fog produced by development at temperatures above 30C is substantially reduced by means of the disulphide compounds corresponding to the above general formula.

The developer described in the cognate co-pending Applications 4646/71 and 1282/72, which is suitable for lith-development comprises a p-dihydroxybenzene developing agent, preferably hydroquinone, an amount of sulphite ions of at least 5 g per litre, and a nitroindazole or nitrobenzimidazole corresponding to one of the following general formulae:

sion speed and of contrast of the image developed by wherein:

incorporating in the lith material an aliphatic, aromatiteor heterocyclic disulphide compound carrying at least one water-solubilizing group in acid or salt form, e.g. a sulpho group or carboxyl group, especially a disulphide compound which corresponds to the following eneral formula:

Y is a nitro substituent in the 5'- er -iosition of the indazole nucleus,

X is hydrogen or a sulpho reap in salt form,

R is hydrogen or a C -C alLyl group,

X is a sulpho group in salt farm,

Y is nitro, and

n is a positive integer l, 2 or 3. the said developer being substantially free from any auxiliary developing agent that shows a superadditive developing effect with the said p-dihydroxybenzene developing agent.

Representative examples of disulphide compounds for use according to the present invention are:

NaO S Na 2 Na S- Q-s-s- Q. -S0 Na CH3 cu 3 Nao s- Q-S-S- G -SO Na SOBNa 9. HOOC-CH -CH2-S] 2 NaO3S--NH-CO-CH 2 1 1 I: HOBS- (CH -NH-CH -CH S- 2 OGO(CH SO3Na 4 1 4 [Nao s-' CH2) 3OCO-CH=CH Q Compounds 1, 2 and 3 can be prepared according to the method described by H. A. Smith, G. Doughty and G. Gorin in J. Org. Chem. 29 (1964) 1484. Compound 4 was prepared as follows:

7.44 g (0.03 mole) of 4,4'-dithioaniline and 16.5 g (0.09 mole) of o-sulphobenzoic anhydride were boiled for 11 hours in 150 ml of pyridine. The solution was concentrated by evaporation whereupon the residue was dissolved in water and neutralized with sodium carbonate. The solution was again concentrated by evaporation and the pyridine residues were removed. The residue was recrystallized from mI of water. Yield: 8 g (40 Melting point: 260C.

Compound 5 can be prepared as described in J. Org. Chem. 27 (1972 2840.

Compound 6 can be prepared as described in US. Pat. No. 3,057,725

Compound 7 can be prepared as described in J. Soc. Chem. Ind. 44 (1925) 196. 1

Compound 8 can be prepared as described in Org. Syn. Coll. Vol. II, 580 (1943).

Compound 9 can be prepared as described in J. Am. Chem. Soc. 57 (1935) 45.

Compound 10 was prepared as follows:

26.9 g (0.1 mole). of the compound with formula (cf. Anal. Chem. 31, 918, (1959) and 4 g (0.1 mole) of soidum hydroxide were dissolved in 250 ml of water. At room temperature, a solution of 15 g (0.1 mole) of sodium iodide and 12.7 g (0.05 mole) of iodine in 100 ml of water was added dropwise. After having left standing overnight, the residue was washed with methanol in order to dissolve sodium iodide. The product was recrystallized from water/methanol.

Yield: 18 g (66 Melting point: 260C.

Compound 11 was prepared as follows:

To a solution of 38 g (0.25 mole) of cystamin (free base) in 250 ml of anhydrous methanol, a solution of 61 g (0.5 mole) of propane sultone in 250 ml of anhydrous methanol was added whereupon the whole was boiled for 3 hours. The hygroscopic oil which precipitated was purified by means of the ion exchanger Amberlite 1R/20.

Yield: 48 g (50 Melting point: 200C.

Compound 12 was prepared as follows:

48.8 g (0.2 mole) of 2-mercaptomethylbenzimidazole-5-sulphonic acid and 21.2 g.(0.2 mole) of sodium carbonate were dissolved in 400 ml of water. A solution of 33.2 g (0.2 mole) of potassium iodide and 25.4 g (0.1 mole) of iodine in 200 ml of water was added dropwise at room temperature whereupon the solution was acidified with an excess of hydrochloric acid. The precipitate formed was purified by dissolution in diluted ammonium hydroxide and reprecipitation by means of hydrochloric acid. Yield: 30 g (60 Melting point: 260C.

Compound 13 was prepared as follows:

153 g (0.5 mole) of compound 8 were suspended in 1500 ml of water and then graduallyneutralized by addition with stirring and heating, of 84 g (1 mole) of sodium hydrogen carbonate. The solution was filtered, concentrated by evaporation and dried till constant weight.

The disodium salt was suspended in 1000 m1 of dimethyl formamide whereupon 122 g (1 mole) of propane sultone were added. The mixture was heated for 2 hours at 120C with stirring and then partially concentrated by evaporation under reduced pressure. The precipitate formed was washed repeatedly with ether and then with acetone whereupon it was dried till constant weight.

Yield: 198 g (66 Melting point: 140C.

Compound 14 was prepared as follows:

This compound was prepared in a similar way as compound 13 starting from 71.6 g (0.2 mole) ofcompound 5 and using 48.8 g (0.4 mole) of propane sultone. Yield: 112 g (87 Melting point: 150C.

Compound 15 was prepared as-follows:

a. To a solution of 139 g (1 mole) of p-nitrophenol in 275 ml of methanol, 82 g (1.25 mole) of 85 percent potassium hydroxide were added portion-wise. The precipitate formed was filtered off by suction, washed with ethanol and dried under reduced pressure.

The p-nitrophenol potassium salt was suspended in 1200 ml of dimethyl formamide whereupon 122. g (1 mole) of propane sultone were added. The mixture was stirred and heated for 6 hours at 160C whereupon it was concentrated by evaporation, stirred with ether and dried.

Yield: 278 g (93 Melting point: above 260C.

b. 149.5 g (0.5 mole) of the compound prepared in step a) were dissolved in 2 litres of water whereupon ml of Raney Nickel were added. The nitro compound was reduced under a hydrogen pressure of 1500 psi at 80C. The Raney nickel was filtered off and the filtrate concentrated to a volume of 100 ml. The precipitate formed was filtered off by suction and washed with ice-water.

Yield: 182 g (68 Melting point: above 260C.

c. 26.9 g (0.1 mole) of the compound prepared in step b) and 7.4 g (0.108 mole) of sodium nitrite were dissolved in 200 ml of water. The solution was added dropwise at a temperature between 0 and 5C to 21 ml of concentrated hydrochloric acid and 120 g of ice. The'solution of diazonium salt was added dropwise at a temperature between 15 and 20C and with stirring to an alkaline sodium disulphide solution prepared by dissolving 3.4 g of sulphur, 26 gof sodium sulphide-9-water and 4 g of sodium hydroxide in 70 ml of water.

The mixture was left standing overnight and then acidified to pH 1 by means of concentrated hydrochloric acid whereupon it was heated for 4 hours on a boiling water-bath. The precipitate of sulphur was filtered off and the filtrate was neutralized and concentrated to a volume of 100 ml. The precipitate was filtered off by suction and purified by continuous extraction with methanol.

Yield: 16 g (59 Melting point: above 260C.

Compound 16 was prepared as follows:

a. benzothiazoline-2-thione-5-sulphonic acid potassium salt.

To a suspension of 298.5 g (1 mole) of 3-nitro-4- chlorobenzenesulphonic acid sodium salt in 350 ml of water, a solution of sodium hydrogen sulphide, prepared by introducing 136 g of hydrogen sulphide in a solution of 960 g (4 mole) of sodium sulphide-9-water in 500 ml of water, was added dropwise at C in minutes.

The mixture was cooled to 40C whereupon 80 ml of carbon disulphide were added dropwise with stirring. The temperature was gradually raised and kept for 5 hours at 9095C.

The mixture was cooled and. filtered whereupon 74.5 g (1 mole) of potassium chloride were added. After acidification with acetic acid, the mixture was diluted with 500 ml of water, and the precipitate was filtered off and recrystallized from water Yield: 215 g (75 Melting point: above 260C.

b. To a solution of 28.5 g (0.1 mole) of benzothiazoline-2-thione-5-sulphonic acid potassium salt in 300 ml of water, a solution of 16.6 g (0.1 mole) of potassium iodide, 12.7 g (0.05 mole) of iodine and 6.9 g (0.05 mole) of potassium carbonate in ml of water was added dropwise at 5060C.

The mixture was stirred for 1' hour and the precipitate formed was filtered off and washed with cold water.

Yield: 20 g (70 Melting point: above 260C.

The amount of disulphide compound used in the lithmaterials in accordance with the present invention may vary within wide limits and depends on the particular compound involved. They are preferably used in amounts comprised between about 5 and about 1000 mg per mole of silver halide.

The silver halides can be dispersed. in the common hydrophilic colloids such as gelatin, casein, zein, polyvinyl alcohol, carboxymethyl cellulose, alginic acid etc. gelatin, however, being preferred.

The silver halide emulsions may be chemically sensitized by effecting the ripening in the presence of small amounts of sulphur containing compounds such as allyl thiocyanate, allyl thiourea, sodium thiosulphate etc. The emulsions may also be sensitized by means of reductors for instance tin compounds as described in our British Pat. Specification No. 789,823 and small amounts of noble metal compounds such as gold, platinum, palladium, iridium, ruthenium and rhodium compounds. Of course, these three types of chemical sensitizers may be used simultaneously.

The emulsions may be used without being spectrally sensitized; however, it is advantageous to spectrally sensitize them according to methods well known in the art to make them ortho-sensitized or panchromatically sensitized. 'Spet'ral sensitizers that can be used are e.g.,

the c'ylnines; ifirocyanines, complex (trinuclear) cyanines'; %i'nplx (trinuclear) merocyanines, styryl dyes, oxondl dyes and the like. Suchlike spectrally sensitizing dyes have been described by F. M. Hamer in The cyanine dyes and related compounds (1964).

The silver halide emulsion of the high-contrast photographic elements according to the present invention may also contain conventional addenda for example, plasticizers, coating aids, fog-inhibiting or emulsion stabilizing'compounds e.g. cadmium salts, and hardeners such as aldehyde hardeners, e.g., formaldehyde, mucochloric acid, glutaraldehyde bis(sodium hydrogen sulphite), maleic dialdehyde, aziridines, dioxan derivatives, and oxypolysaccharides.

Development of the lith-type silver halide materials of the present invention preferably occurs in the presence of polyoxyethylene compounds, which may be present either in the lith-material or in the developing solution or in both. These polyoxyethylene compounds include any polymeric compound comprising a polyethylene oxide chain e.g. polyethylene glycol having a molecular weight of 1500 or more and other ethylene oxide compounds as described amongst others in the United Kingdom Patent specification Nos. 600,058 871,801 920,637 940,051 945,340 949,643

991,608 1,015,023 1,091,705 1,107,022 1,147,817 1,162,135 1,184,434 in the published German Patent applications Nos. 1,141,531 1,188,439 and in the U.S. Pat. Nos. 1,970,578 2,240,472 2,423,549 2,441,389 and 3,518,085.

The lith-emulsion and/or lith-developer may further contain onium and polyonium compounds, preferably of the ammonium, phosphonium and sulphonium type or mixtures thereof. Specific onium compounds are e.g. dodecyl-trimethyl. ammonium p-toluene sulphonate, nonyl pyridinium perchlorate, l-m-nitrobenzylquinolinium chloride, l-dodecylpyridinium chloride, N,N'-tetramethylene-bispyridinium chloride, N,N- hexadecamethylene-bispyridinium perchlorate, nnonyl dimethyl sulphonium p-toluene sulphonate, tetramethylene bistriethyl phosphonium bromide, lauryl triethyl phosphonium bromide, onium salts of polyoxyalkylenes e. g. polyoxyalkylene bispyridinium salts etc. Further examples of suitable onium compounds can be found in U.S. Pat. Nos. 2,271,662 2,271,263 2,275,727 2,288,226 9.944,898 2,944,900 and The silver halide emulsions of use according to the invention may be coated on a wide variety of supports. Hydrophilic colloid layers may be coated on one or both sides of the support, if desired. Typical supports are cellulose nitrate film, cellulose ester film, polyvinyl acetal film, polystyrene film, poly(ethylene terephthalate) film, and related films of resinous material, as well as glass, paper, metal and the like. Supports such as paper, which are coated with a-olefin polymers, particularly polymers of a-olefins containing two or more carbon atoms, as exemplified by polyethylene, polypropylene, ethylenebutene copolymers and the like may also be employed.

The following examples illustrate the present invention.

EXAMPLE 1 A fine-grain silver halide emulsion of the lith-type containing 75 mole percent of silver chloride and 25 mole percent of silver bromide was prepared in the.

hydroquinone 13 g formaldehydebisulphite 50 g sodium carbonate g potassium bromide 0.5 g sodium carbonate to obtain a pH of 10 a polycondensation product of polyethylene glycol (average molecular weight 1000) and triethylphosphate prepared as described in preparation 3 of U.K.Pat. Specification 945,340 0.5 g

The values of the fog produced are listed in the table below.

Table Fog produced after development Compound added for 2 min. for 4 min.

The emulsion speed was not affected to a noteworthy extent.

EXAMPLE 2 Example 1 was repeated with the difference that development now took place for 2 and 4 min. at 32C in a Metol-hydroquinone developer of the following composition:

water Metol( p-monomethylaminophenol sulphate) 1.5 g anhydrous sodium sulphite 50 g hydroquinone 6 g anhydrous sodium carbonate 32 g potassium bromide 2 g water to make 1000 ml The results attained were listed in the following table.

Table Fog produced after development Compound for 2 min. for 4 min.

EXAMPLE 3 An emulsion of the type described in example 1 was divided into several aliquot portions. To each of these portions, except one, a disulphide compound was added as listed in the table below in the amount given.

After coating on a support as described in Example 1 the materials were stored for 36 hours at 57C and 34 percent relative humidity.

The values of fog produced after exposure and development for 2 min. as described in example 1, are listed in the table below.

1. Method of producing a high contrast image by development in a developer which contains hydroquinone or a hydroquinone drivative having a low sulphite ion content and at a temperature above 30C. of an exposed photographic light-sensitive lithmaterial which will provide a characteristic curve with a short toe and high gamma and which will produce sharply defined images with high density extending to the edges of lines and dots comprising a support having thereon at least one light-sensitive high contrast silver halide emulsion having a fine grain, which comprises at least 50 mole percent of silver chloride and at least 5 mole percent of silver bromide, wherein the said material comprises a disulphide compound of the formula:

wherein:

each of A, and A represents an alkylene group, an

arylene group, or a benzthiazolyl group, and each of X and Y represents a water-solubilizing group in acid or salt form, or a substituent carrying a water-solubilizing group, said substituent forming a bridging group between the water-solubilizing group and A, and A selected from a saturated or unsaturated aliphatic group, an aromatic group and a benzimidazolylene group. 2. Method according to claim 1, wherein the said disulphide compound has the formula:

wherein each of A, and A stands for C,-C alkylene and each of X and Y stands for a water-solubilizing group in acid or salt form. I 3. Method according to claim 1, wherein the said di sulphide compound has the formula:

wherein each of A, and A stands for phenylene and each of X and Y stands for a water-solubilizing group in acid or salt form. 4. Method according to claim 1, wherein the said disulphide compound has the fiormula:

wherein each of A, and A stands for C,C alkylene and each of X and Y stands for a substituent carrying a water-solubilizing group in acid or salt form, the said substituent being a bridging benzimidazolylene, alkylene carbamoyl, alkylene sulphamoyl, arylene carbamoyl, arylene sulphamoyl, alkylene amino, alkylene acylamino or arylene acylamino group between the water-solubilizing group and the alkylene groups represented by A, and A 5. Method according to claim 1, wherein the said disulphide compound has the formula:

wherein each of A, and A is a phenylene group and each of X and Y stands for a substituent carrying a watersolubilizing group in acid or salt form, the said substituent being a bridging alkyleneoxy, alkyleneoxycarbonyl, vinylene, alkyleneoxycarbonylvinyl, alkylene carbamoyl, alkylene sulphamoyl, arylene carbamoyl, arylene sylphamoyl, alkylene acylamino or arylene acylamino group between the water-solubilizing group and the phenylene groups represented by A, and A 6. Method according to claim 1, wherein the said disulphide compound is present in the silver halide emulsion in an amount comprised between 5 mg. and 1000 mg per mole of silver halide.

7. Method according to claim 1, wherein the said material also comprises a polyoxyethylene compound.

8. Method according to claim 1, wherein the exposed material is developed in a lith-type developer, which comprises as the only developing agent hydroquinone and which comprises a low sulphite ion content. 

1. METHOD OF PRODUCING A HIGH CONTRAST IMATE BY DEVELOPMENT IN A DEVELOPER WHICH CONTAINS HYDROQUINONE OR A HYDROQUINONE DRIVATIVE HAVING A LOW SULPHITE ION CONTENT AND AT A TEMPERATURE ABOVE 30*C. OF AN EXPOSED PHOTOGRAPHIC LIGHTSENSITIVE LITHMATERIAL WHICH WILL PROVIDE A CHARACTERISTIC CURVE WITH A SHORT TOE AND HIGH GAMMA AND WHICH WILL PRODUCE SHARPLY DEFINED IMAGES WITH HIGH DENSITY EXTENDING TO THE EDGES OF LINES AND DOTS COMPRISING A SUPPORT HAVING THEREON AT LEAST ONE LIGHT-SENSITIVE HIGH CONTRAST SILVER HALIDE EMULSION HAVING A FINE GRAIN, WHICH COMPRISES AT LEAST 50 MOLE PERCENT OF SILVER CHLORIDE AND AT LEAST 5 MOLE PERCENT OF SILVER BROMIDE, WIEREIN THE SAID MATERIAL COMPRISES A DISULPHIDE COMPOUND OF THE FORMULA:
 2. Method according to claim 1, wherein the said disulphide compound has the formula: X - A1 - S - S - A2 - Y wherein each of A1 and A2 stands for C1-C7 alkylene and each of X and Y stands for a water-solubilizing group in acid or salt form.
 3. Method according to claim 1, wherein the said disulphide compound has the formula: X - A1 - S - S - A2 - Y wherein each of A1 and A2 stands for phenylene and each of X and Y stands for a water-solubilizing group in acid or salt form.
 4. Method according to claim 1, wherein the said disulphide compound has the formula: X - A1 - S - S - A2 - Y wherein each of A1 and A2 stands for C1-C7 alkylene and each of X and Y stands for a substituent carrying a water-solubilizing group in acid or salt form, the said substituent being a bridging benzimidazolylene, alkylene carbamoyl, alkylene sulphamoyl, arylene carbamoyl, arylene sulphamoyl, alkylene amino, alkylene acylamino or arylene acylamino group between the water-solubilizing group and the alkylene groups represented by A1 and A2.
 5. Method according to claim 1, wherein the said disulphide compound has the formula: X - A1 - S - S - A2 - Y wherein each of A1 and A2 is a phenylene group and each of X and Y stands for a substituent carrying a water-solubilizing gRoup in acid or salt form, the said substituent being a bridging alkyleneoxy, alkyleneoxycarbonyl, vinylene, alkyleneoxycarbonylvinyl, alkylene carbamoyl, alkylene sulphamoyl, arylene carbamoyl, arylene sylphamoyl, alkylene acylamino or arylene acylamino group between the water-solubilizing group and the phenylene groups represented by A1 and A2.
 6. Method according to claim 1, wherein the said disulphide compound is present in the silver halide emulsion in an amount comprised between 5 mg. and 1000 mg per mole of silver halide.
 7. Method according to claim 1, wherein the said material also comprises a polyoxyethylene compound.
 8. Method according to claim 1, wherein the exposed material is developed in a lith-type developer, which comprises as the only developing agent hydroquinone and which comprises a low sulphite ion content. 